Joysticks for use as computer input devices have been available for over two decades. To facilitate operation in two directions, a popular electromechanical configuration employs orthogonal potentiometers physically coupled to a moveable element. As one example of many, U.S. Pat. No. 4,156,130 describes a joystick mechanism for transducing vector motion of an end of a joystick into its X and Y components. The apparatus includes X- and Y-potentiometers, each having a body and a shaft, a rod connecting the shaft of the X-potentiometer to the body of the Y-potentiometer so that the shafts of the X and Y-potentiometers lie at right angles to each other, and a joystick having one end attached to the shaft of the Y-potentiometer and which is oriented such that its effective axis lies at a right angle relative thereto.
One problem with potentiometer-based joysticks and other input devices is that the potentiometers are relatively expensive and include moving parts that may become dirty or worn, resulting in intermittent behavior. As such, alternative approaches have been tried using optical, Hall-effect, and capacitive transducers having fewer moving parts.
An early capacitive joystick is described in U.S. Pat. No. 4,305,007. According to this patent, four sensing electrodes of approximately equal capacitance are symmetrically arranged into pairs of opposing sensing electrodes within a common plane. Two pairs of resistors are electrically connected to receive discharge currents originating from each pair of opposing sensing electrodes, with each discharge current being a function of corresponding sensing electrode capacitance. A detector circuit electrically connected to both pairs of resistors for simultaneously detecting both continuous discharge currents from each pair of resistors, detecting differences therebetween, and generating two electrical outputs respectively.
U.S. Pat. No. 5,576,704 describes a capacitive joystick apparatus applicable to the control of work implements on machines which perform digging or loading functions such as excavators, backhoe loaders, and front shovels. The joystick includes a control shaft having an operator handle and a base. An actuating body is rigidly attached to the control shaft, and a cardan joint is provided to pivotally mount the control shaft to the base. A plurality of electrically non-contacting sensors sense the relative position of the shaft relative to the base. The sensors include a pair of spaced apart electrodes establishing an electrostatic capacity with each other, and a dielectric body being disposed between the electrode pair. Accordingly, as the control shaft pivots, the actuating body engages the dielectric body which moves the dielectric body relative to the electrode pair thereby modifying the capacitance of the sensor.
In U.S. Pat. No. 5,421,694, a non-contacting joystick includes a control shaft universally movable about a Z-axis. A spherical conducting body is attached to an end of the control shaft. A plurality of conducting plates are disposed circumjacent to the spherical body. A charging power supply supplies electrical energy of a first polarity to the spherical body and electrical energy of a second polarity to the plurality of conducting plates. Each conducting plate forms a variable capacitor with the spherical body. The capacitance value of each variable capacitor is a function of the displacement of the spherical body relative to the Z-axis. A circuit produces a plurality of position signals, each position signal being responsive to a capacitance value of a respective variable capacitor. The position signals indicate the relative position of the spherical body.
The computer pointing device described in U.S. Pat. No. 5,949,354 uses capacitors installed in various directions to generate pointing signals. The pointing device comprises a circuit board, a cap, and a detecting unit. The circuit board comprises a center point, a first conducting plate installed in a first direction and a second conducting plate installed in a second direction. The cap is movably installed above the center point of the circuit board. The bottom side of the cap has a top conducting plate which forms first and second capacitors with the first and second conducting plates separately. The detecting unit is electrically connected to the top, first and second conducting plates to detect the capacitance of the first and second capacitors and generate corresponding pointing signals to reflect the position of the cap in the first and second directions.
In U.S. Pat. No. 5,911,627, a joystick having an electromagnetic element is coupled to a movable stick, with at least a pair of orthogonal coils on an underlying substrate. The movement of the stick is detected by the amount of overlap of the electromagnetic element and the coils in each direction. The quality factor of the coil changes as more or less of the coil is overlapped, which can be measured by an electric circuit to determine the direction of movement and the amount of movement of the joystick. The coils could be made from traces on a printed circuit board (PCB), provided the use of a high enough (greater than 1 MHz) driving frequency, eliminating the need for a large, expensive wound coil.
In U.S. Pat. No. 5,786,997, a capacitively coupled, six axis joystick employs a sensor electrode having a perpendicular pair of slots and a fixed electrode assembly having capacitor electrodes formed on three mutually orthogonal surfaces of planar circuit boards that are complementarily nested within the slots of the sensor electrode. When nested together, the capacitor electrodes are separated from faces of the sensor electrode by spacings that depend on the rotational and translational movements of the sensor electrode relative to the electrode assembly. A signal generator and address decoder sequentially apply an alternating signal to the capacitor electrodes. The alternating signal is coupled to the closest associated faces of the sensor electrode to a degree dependent on the rotation- and translation-induced spacings. A controller detects and processes each coupled signal voltage to determine a degree of deflection of the sensor electrode in the X-, Y-, Z-, roll-, pitch-, and yaw-axis directions.
In existing capacitive joysticks, one electrode of a capacitive transducer is moved relative to a fixed electrode. Although the result is a simple physical arrangement, movement and/or pivoting of the capacitor electrode itself presents certain disadvantages, including wide fluctuations in the signal to be sensed, and variation between units, resulting in operational instability and the need for calibration. In certain unrelated types of devices, including control switches and shaft encoders, an element is rotated or translated relative to one or more fixed capacitor plates, resulting in accurate, reproducible operation.
A capacitance sensing system for sensing the rotary position of a rotating shaft, particularly one having limited rotary motion is described in U.S. Pat. No. 4,864,295. The system uses at least four capacitances comprising fixed capacitance plate members, one of which is preferably made of four arcuate segments enclosing the shaft and the other of which is a ring member enclosing the shaft and displaced therefrom along the shaft. A dielectric member is attached to the shaft between the fixed plate members. The capacitance value of the four capacitances change as the shaft rotates in such a manner that the capacitance changes produce an output voltage which represents the rotary position of the shaft, which output voltage is insensitive to radial motions of the shaft.
U.S. Pat. No. 5,537,109 resides in a variable capacitance, high-precision, stable transducer for detecting the position of a moving member. The device includes a first stationary conducting surface connected to a source, a second surface with at least two conducting, sensing regions, and a third movable conductive surface located between the first surface and the second surface and connected to the moving member. The third surface is adapted to modulate charge transferred from the source surface before reaching the sensing regions. The difference of signals detected at the individual sensing regions is utilized to determine the position of the moving member and the sum of the signals is utilized to achieve appropriate correction in a feedback loop connected to the source.
U.S. Pat. No. 5,598,153 teaches a measuring device for the measurement of a rotor angle including a capacitive angular displacement transducer generating an output that varies with an angular displacement of a shaft. A first stator has a plurality of transmitting electrodes to generate electric fields within the transducer due to excitation signals applied to the plurality of transmitting electrodes which are electrically conducting circle sectors of equal area which are electrically isolated from each other and which completely cover a rotational angle of 2π on the first stator. A second stator is parallel and coaxial to the first stator, and includes a conductive ring electrode receiving excitation from the first stator and producing an electric output signal. A rotor, located coaxially and parallel to the first stator and the second stator, has at least one rotor blade in the form of circle sectors, the central angle of each rotor blade being equal to at least the sum of the central angles of two sectors of the first stator. A signal processing unit determines the rotor angle in accordance with angle dependent transfer functions.